The present invention relates generally to a vehicular AC generator including a silent-pole type rotor supported by brackets. More particularly, the present invention relates to improvement of a vehicular AC generator of the foregoing type including front and rear fans secured to the opposite ends of magnetic pole cores wherein the composite air stream sound generated by both the fans can substantially be attenuated.
To facilitate understanding of the present invention, a conventional vehicular AC generator will be described below with reference to FIG. 3 and FIG. 4.
FIG. 3 is a vertical sectional view of the generator and FIG. 4 is a front view of the same. In FIG. 3, reference numeral 1 designates a stator. The stator 1 is constructed of a stator core 2 and a stator coil 3. Reference numeral 4 designates a rotor. The rotor 4 is constructed in the following manner. Reference numerals 5 and 6 designate magnetic pole cores each having a different polarity. Tooth-shaped magnetic pole portions 5a and 6a of the magnetic pole cores 5 and 6 are alternately arranged in the circumferential direction in the projected state. Reference numeral 7 designates an excitation coil, reference numeral 8 designates a rotational shaft on which the magnetic pole cores 5 and 6 are fixedly mounted, reference numeral 9 designates a pair of slip rings which are fixedly mounted on the rotational shaft 8 with an electrical insulating sleeve (not shown) interposed there-between, and reference numerals 10 and 11 designate fans which are secured to the magnetic pole cores 5 and 6, respectively.
In addition, reference numeral 12 designates a front bracket and reference numeral 13 designates a rear bracket. Both the brackets 12 and 13 are connected to the stator core 2 by tightening a plurality of bolts 14 of which only one is shown in the drawing. To maintain proper ventilation for the purpose of cooling the generator, a plurality of air intake holes 12a are formed around the inner circumference of the front bracket 12 and a plurality of air outlet holes 12b are formed around the outer circumference of the same. Similarly, a plurality of air intake holes 13a are formed around the inner circumference of the rear bracket 13 and a plurality of air outlet holes 13b are formed around the outer circumference of the same for the purpose of maintaining ventilation. The rotational shaft 8 is rotatably supported by the front bracket 12 and the rear bracket 13 with the aid of bearings 15 and 16. Reference numeral 17 designates a pulley which is fixedly mounted on the rotational shaft 8. As an engine (not shown) operates, the rotational force generated by the engine is transmitted to the rotor 4 via a belt (not shown) and the pulley 17.
Reference numeral 18 designates a rectifier for rectifying AC voltage induced by the stator coil 3 to DC voltage, and reference numeral 19 designates a voltage regulator for detecting an output voltage from the rectifier 18 to adjust a terminal voltage to a predetermined value by controlling the excited current. Reference numeral 20 designates a brush holder. The brush holder 20 serves to bring a brush 21 held thereby in pressure contact with the slip rings 9 so as to allow the excited current to be supplied to consumer' units or instruments via the brush 21.
With the AC generator constructed in the above-described manner, as the rotor 4 is rotated, AC voltage is induced in the stator coil 3, causing electric power to be supplied to consumer's units or instruments while generating heat. To cool the stator 1 and the rotor 2, the front fan 10 and the rear fan 11 are rotated, whereby the air in the generator is ventilated to the outside.
As the front fan 10 is rotated, cooling air is first introduced into the generator through the air intake holes 12a on the front bracket 12 in the A arrow-marked direction to cool the stator 1, and thereafter, it is exhausted to the outside through the air outlet holes 12b. On the other hand, as the rear fan 11 is rotated, cooling air is first introduced into the generator through the air intake holes 13a on the rear bracket 13 in the B arrow-marked direction to cool the rectifier 18, the voltage regulator 19, the commutator section and the stator 1, and thereafter, it is exhausted to the outside through the air outlet holes 13b.
FIG. 5 is a sectional view of other conventional AC generator of which structure is identical to that of the generator shown in FIG. 3 with the exception that slip rings 9, a rectifier 19 and a brush holder 20 are arranged outside of a rear bracket 23. A plurality of air intake holes 23a are formed around the inner circumference of the rear bracket 23 and a plurality of air outlet ports 23b are formed around the outer circumference of the same. In FIG. 5, reference numeral 24 designates a cover which is attached to the outer end of the rear bracket 23. In addition to the air intake holes 23a, a plurality of air intake holes 24a are formed through the cover 24. As the rear fan 11 is rotated, cooling air is first introduced into the generator through the air intake holes 24a on the cover 24 in the C arrow-marked direction and then flows through the air intake holes 23a on the rear bracket 23, and thereafter, it is exhausted to the outside through the air outlet holes 23b.
Referring to FIG. 4 again, the generator includes twelve magnetic poles and twelve air intake holes 12a on the front bracket 12, while the front fan 10 has ten blades 10a.
FIG. 6 is a front view of a front fan for another conventional AC generator and FIG. 7 is a front view of a rear fan of the same. As shown in FIG. 6, the generator includes twelve magnetic pole cores 5 and 6, while the front fan 10 has twelve blades 10a. In the drawing, reference numeral 10b designates a reinforcement rib which is press-formed on each blade 10a. On the other hand, as shown in FIG. 7, the rear fan 11 has ten blades 11a. In the drawing, reference numeral 11c designates projected parts which are press-formed on the rear side of the rear fan 11 so as to allow lead wires for an excitation coil 7 to extend therethrough.
FIG. 8 is a front view of a front fan for another conventional vehicular AC generator, particularly illustrating case that the generator includes sixteen magnetic pole cores and the front fan 10 has ten blades 10a wherein the magnet pole cores are not shown in the drawing for the purpose of simplification of illustration.
With each of the conventional vehicular AC generators constructed as described above, there arises a problem that the degree component of the air stream sound generated by both the fans coincides with the degree component of the air stream generated by the magnet pole cores, resulting in the sound level of the composite air stream sound being elevated, since the generator includes an even number of magnetic poles (twelve magnetic poles, sixteen magnetic poles or the like), the front fan 10 has an even number of blades (ten blades, twelve blades, fourteen blades or the like), and the rear fan 11 has an even number of blades (ten blades, twelve blades or the like). In the case of a three-phase AC generator, the stator core 2 has thirty six slots when the generator includes twelve magnetic poles and it has forty eight slots when it includes sixteen magnetic poles on the assumption that each magnetic pole has one slot per each phase, while each fan has twelve blades. Thus, there arises a similar problem that the degree component of the air stream sound generated by the slots on the stator core coincides with the degree component of the air stream sound generated by both the fans, resulting in the sound level of the composite air stream sound being elevated.